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Yokosuka K4Y

The Yokosuka K4Y, also known as the Navy Type 90 Seaplane Trainer, was a floatplane trainer utilized by the Japanese military during the 1930s.

This single-engined, two-seat biplane was produced in a quantity of 211 units between 1933 and 1940, serving as the primary floatplane trainer for the Imperial Japanese Navy throughout the duration of the Second World War.

In 1930, the Imperial Japanese Navy Air Service identified the need for a replacement to their existing seaplane trainer, the Yokosuka K1Y or Type 13 Seaplane Trainer, which had been in use since 1925.

The First Naval Air Technical Arsenal, based in Yokosuka, was tasked with designing a new model.

The design team, led by Jiro Saha and Tamefumi Suzuki, developed a single-bay biplane with a welded steel-tube fuselage and wooden wings, marking the first Japanese-designed aircraft to feature such a fuselage.

Yokosuka constructed two prototypes, powered by 90 hp (67 kW) Hatakaze four-cylinder air-cooled inline engines in 1930.

Following successful testing, a version powered by a 130 hp Gasuden Jimpu radial engine was ordered into production as the Navy Type 90 Seaplane trainer, with the short designation K4Y1.

Production commenced at Watanabe in May 1933, with 156 units produced by 1939.

Production then shifted to Nippon Hikoki, who built an additional 53 units in 1939-1940.

The K4Y1 began replacing the K1Y in 1933 and remained the principal basic seaplane trainer for the Imperial Japanese Navy Air Service throughout the Pacific War.





9.05 m (29 ft 8 in)


10.90 m (35 ft 9 in)


3.51 m (11 ft 6 in)

Wing area

29.5 m2 (318 sq ft)

Empty weight

740 kg (1,631 lb)

Gross weight

990 kg (2,183 lb)


1 × Gasuden Jimpu 2 seven-cylinder air-cooled radial engine,

97 kW (130 hp)


Maximum speed

163 km/h (101 mph, 88 kn) at sea level

Cruise speed

93 km/h (58 mph, 50 kn)


310 km (200 mi, 170 nmi)


3 hours 30 min

Service ceiling

3,460 m (11,350 ft)

Time to altitude

29 min 20 sec to 3,000 m (9,800 ft).

Japanese Aircraft, 1910-1941-Robert Mikesh & Shorzoe Abe
The Mainichi Newspapers Co Ltd
Yushukan War Memorial Museum
Japanese Aircraft of the Pacific War-Rene Francillon,
Japanese Aircraft-John Stroud,
Japanese Military Aircraft Illustrated.


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